Systems and methods for identifying polarization/quadrature channels in dual- polarization coherent optical transmission

Abstract

Described are systems and methods for identifying the phase and polarization of independent modulation streams in quadrature channels of a coherent transmission system by using digital code. As a result, phase rotation and polarization of streams that during transmission may have become rotated and swapped around in the channel are correctly labeled and depermuted according to a known and predictable order.

What is claimed is: 
     
       1. A method for identifying phase and polarization in a coherent transmission system, the method comprising:
 in response to receiving quadrature channel data that have been labeled with a digital code, generating phase rotation data in one or more quadrature channels; and 
 using a correlation function to obtain a mapping of modulated data, the mapping indicating whether polarization channels in the quadrature channel data have been swapped. 
 
     
     
       2. The method according to  claim 1 , wherein the digital code is a phase-shift-encoded using different phases of a same sequence of symbols to label polarity and identity of the quadrature channel data. 
     
     
       3. The method according to  claim 2 , wherein the sequence of symbols is derived from the output of a maximal length linear feedback shift register. 
     
     
       4. The method according to  claim 2 , wherein two sequences of symbols having different generator polynomials have a same length. 
     
     
       5. The method according to  claim 1 , further comprising increasing a chip duration of the digital code to reduce a processing speed of a matched filter detector. 
     
     
       6. The method according to  claim 1 , wherein the quadrature channel data and the digital code are received by a correlation peak detector that comprises matched filters that use the digital code as a set of tap weights that are passed through a sliding integrator to a perform peak detection. 
     
     
       7. The method according to  claim 1 , wherein a phase in the phase rotation data is defined relative to an intentional gap in correlation peaks. 
     
     
       8. An coherent transmission system comprising:
 a digital code generator that generates an output comprising a sequence of symbols that have a cyclic autocorrelation that substantially approximates an impulse function; and 
 a combiner coupled to the digital code generator, the combiner, in response to receiving modulated data, combines the modulated data with the sequence of symbols to label polarity and identity of the modulated data, the coherent transmission system outputs labeled modulated data. 
 
     
     
       9. The coherent transmission system according to  claim 8 , further comprising a correlation peak detector that uses one or more void possible cyclic positions to identify correlation peaks as the beginning of the sequence of symbols, the correlation peak detector generating correlation data that is applied to a phase rotation detector to obtain phase rotation data. 
     
     
       10. The coherent transmission system according to  claim 9 , further comprising a reference pattern detector that, in response to receiving the correlation data, generates a mapping of the modulated data that indicates whether polarization channels have been swapped. 
     
     
       11. The coherent transmission system according to  claim 9 , wherein the phase rotation uses an angle of a correlation coefficient to determine phase rotations in multiples of 90 degree rotation angles. 
     
     
       12. The coherent transmission system according to  claim 9 , wherein an order of the correlation peaks indicates whether polarization channels in the modulated data have been swapped during transmission. 
     
     
       13. The coherent transmission system according to  claim 12 , wherein the phase rotation and the order are used to remap the modulated data. 
     
     
       14. The coherent transmission system according to  claim 12 , further comprising a remapping circuit comprising a decision circuit that uses threshold detection to perform remapping or depermutation operations according to the order of the correlation peaks. 
     
     
       15. The coherent transmission system according to  claim 14 , wherein the remapping circuit comprises a multiplexer that uses a map of the modulated data to remap output channels according to a lookup table. 
     
     
       16. The coherent transmission system according to  claim 15 , wherein the remapping circuit comprises a switch matrix that applies information in the lookup table to the modulated data to remap the output channels. 
     
     
       17. The coherent transmission system according to  claim 15 , wherein the digital code generator is implemented as a pilot pseudo-noise code generator.